1. Field of the Invention
The present invention relates to a non-aqueous electrolyte secondary battery and a method for producing an anode therefor. In particular, the present invention is concerned with a carbon material for constituting the anode.
2. Description of the Prior Art
The non-aqueous electrolyte secondary batteries having anodes configured with an alkali metal such as lithium and the like have a high electromotive force (EMF), and are expected to have a high energy density as compared with that of the conventional nickel-cadmium batteries or lead-acid batteries. Therefore, researches have been made increasingly to develop the batteries of this category. In particular, a number of such researches have heretofore been made on the non-aqueous electrolyte battery having an anode configured with lithium. If Li as the alkali metal is used for its anode in a metal state, dendrite formation occurs in the course of charging process of the batteries configured with Li anodes, which renders problems of short-circuiting and poor reliability in such batteries.
In order to cope with these problems, an investigation has been made on an anode configured with an alloy of lithium of alkali metal and aluminum or lead. In such alloy anode, Li is absorbed in the anode alloy in the course of charging process and no dendrite develops. Thus, a battery having a higher reliability is produced. However, the discharge potential of such alloy anode is more noble by about 0.5 V than that of metal Li, the cell voltage of the battery configured with this alloy anode is lower by 0.5 V than that of the battery configured with the metal Li anode, which results in a lower energy density.
On the other hand, researches have been made on an anode configured with an intercalation compound of carbon which contains Li atoms intercalated therein. In this compound anode, Li is intercalated between the layers of carbon by charging, whereby the dendrite formation is effectively prevented. The discharge potential of this compound anode is noble only by about 0.1 V as compared with that of metal Li anode, and therefore, the decrease in the cell voltage of the battery is small. For the above-stated reasons, this compound anode can be regarded as a more preferable anode.
This compound anode, however, has a serious disadvantage. That is, the maximum amount of Li that can be intercalated in the carbon by charging is limited to the amount corresponding to a stoichiometric amount of C.sub.6 Li, and in that case, the electric capacity of this compound anode amounts to 372 Ah/kg. In the charging-discharging cycle of a normal battery, the electric capacity of the anode is as small as 230 Ah/kg.